[Trial of a live vaccine against babesiasis in sheep].

A flock of 86 weaned lambs was used in field conditions to test the vaccination against babesiasis in sheep, using blood containing up to 5 per cent Babesia ovis-infected erythrocytes, referred to as a "live vaccine". The blood was obtained through successive passages performed with the vaccinal strain in four spleenectomized lambs with the parallel treatment of the latter with tetracyclin. The application of the vaccine at rates of 1.75 X 10(7); 3.5 X 10(7); and 7 X 10(7) Babesia organisms was well tolerated, the animals responding with a temperature reaction only. The immunity acquired proved sufficiently stable against the experimental challenge with a triple dose of the maximal vaccinal one as well as against the natural infection to which the flock was exposed within the period between the third and sixth month following vaccination. At the same time babesiasis in an enzootic form developed in the control flock, the test flock showing no cases of diseased animals. The complement-fixing antibodies established from the tenth up to the 90th day after the vaccination was carried out served as an index of the immunity status. The optimal vaccination dose is suggested to be that containing 3.5 X 10(7) Babesiae.